In an ACL procedure, soft tissue, such as a ligament graft, is affixed to the femur and the tibia. The tissue graft is implanted by securing one end of the tissue graft through a passage formed in the femur, and the other end of the graft through a passage formed in the tibia. Generally, a fixation device (e.g., an interference screw) is used to affix each end of the tissue graft to the bone.
A number of devices are commercially available to affix the graft to the bone. For example, the IntraFix ACL® Tibial Fastener System (manufactured by DePuy Synthes, a Johnson & Johnson Company, Warsaw, Ind., USA) features a two-part system including an expandable polypropylene sheath that receives a PEEK screw. The sheath expands and holds the graft in place as the screw is inserted into the sheath. The IntraFix® system attempts to more accurately replicate the native ACL by using a screw to spread apart an integral four quadrant sheath. This acts to compress the four tendon strands against the bone. The system may be considered by some to be easier to use than other alternatives, and does not need additional drill holes. However, the IntraFix® device does require additional accessories, additional people to perform the procedure, and the four quadrant design does not accommodate certain grafts with two tendon strands, such as the tibialis.
Various patents describe devices to affix the graft to bone. For example, U.S. Pat. No. 7,309,355 to Donnelly et al. describes a radially expandable sheath having a substantially closed distal end with at least two sidewalls extending proximally therefrom and defining a central lumen. Each sidewall can have a substantially concave outer surface adapted to seat a graft member, and each side wall is at least partially separated by a longitudinally oriented slot that extends from a proximal end along a substantial length of each sidewall. The slot preferably terminates at a position just proximal to the distal end. The device can also include a sheath expander that is adapted to be disposed in the central lumen of the radially expandable sheath configured to flex the sidewalls to radially expand the sheath so as to fix a graft member within a bone tunnel.
U.S. Pat. No. 8,562,680 to Hays et al. describes another radially expandable sheath. In the '680 patent, a graft ligament anchor comprises a graft ligament engagement member disposed in an opening in a bone. The graft ligament engagement member is arranged to receive a graft ligament alongside the engagement member and a locking member for disposition in the opening, and is at least in part engageable with the graft ligament engagement member. Movement of the locking member in the opening causes the locking member to urge the engagement member, and the graft ligament therewith, toward a wall of the opening to secure the graft ligament to the wall of the opening.
US Publication No. 2012/0109299 to Li et al. describes another system and method for ligament reconstruction including an implant having a sheath, a first ledge, a second ledge, a first anchor and a second anchor. The sheath has an exterior surface and an interior surface, wherein the interior surface of the sheath forms a lumen configured to receive a sheath expander. The first ledge and the second ledge are configured to separate the ligaments and act as an anchor for the sheath in the bone tunnel. The first anchor and the second anchor are configured to engage the ligaments and be expandable outwards away from the lumen to provide fixation in a bone tunnel. When the implant receives the sheath expander, the ligaments can be separated, positioned, and secured in the bone tunnel.
U.S. Pat. No. 8,663,325 to Graf et al. describes another soft tissue graft anchor including a plurality of prongs. Each prong includes a distal end and a proximal end, wherein the prongs are coupled at their distal ends to form an inner cavity having an opening. At least one of the prongs includes a fin. The fin extends perpendicular to a longitudinal axis of the prong and includes a pointed end. A tissue graft anchor assembly, a method for tissue repair, and instrumentation for use therewith is also disclosed.
The above mentioned devices generally rely on the elasticity of the sheath walls to deform. The wall material must have a relatively high elasticity. The wall must also predictably bend in situ when the inner screw member is deployed to expand into the graft.
U.S. Pat. No. 7,967,861 to Montgomery et al. describes another expandable sheath for affixing tissue to bone. The '861 patent describes a material fixation system which comprises two sheath portions defining a space therebetween, and a hinge for attaching the sheath portions together along one side thereof. An insertion member, preferably a tapered screw, is insertable into the space for expanding the sheath portions laterally outwardly in order to urge a soft tissue graft against an adjacent bone surface. Although the '861 patent does include a hinge for opening two sheath portions against the graft legs, the side position of the hinge is not optimal because it may cause a shearing force on the graft legs in addition to a compression force.
The above mentioned devices can be improved to more reliably secure the soft tissue in a bone. This is especially important concerning the tibia because the tibial side becomes the weakest link in the reconstructed anatomy. Furthermore, there is no back up fixation in the event the tibia side fails.